Coaxial switch



Dec. 15, 1959 J. E. JENNINGs EI'AL 2,917,596

coAxIAL SWITCH Filed Nov. 1, 1957 tb e/'r ATTORNEY United States Patent C 2,911,596 coAXrAL SWITCH Jo Emmett Jennings and Ted N. Tilman, San Jose, Calif.,

assignors to Jennings Radio Manufacturing Corporation, San jJose, Calif., a corporation of California Application` November 1, 1957, Serial No. 694,028 l1o Claims. (cl. zoo-sz) Another object is the provision of a vacuum coaxial.

switch which may be remotely controlled without creatingshock waves. in the circuit or unduly disturbing the standing-wave-ratio.

Still another object is the provision of a vacuum coaxial switch in which capacitance between adjacent circuits is negligible.V

A still further object is the provision of a coaxial switch structure'easily converted froma characteristic high impedancel to one of relativelyI low impedance.

TheV invention possesses other objects some of which with the foregoing will be brought out in the following description of the invention. We do notlimit ourselves to'the showing made by the said description and the drawings, since we may adopt Variant forms of the invention within the scope of the appended claims.

Referring to the drawings:

l Fig; lis a plan view of the assembledy switch. The interconnection of the outer. housing. of the switch with the outer conductor of the transmission line is indicated by dash lines.

Fig. 2 is a horizontal sectional View taken in the plane indicated'by the line 2 2 of Fig. 3.

Fig.` 3 is a fragmentary vertical sectional .View taken in the plane indicated by the lne`3-3 of Fig. l.

Fig. 4 is a fragmentary vertical sectional view taken in the same plane as Fig. 3, and showing a modified.

arrangement of actuating means.

All iigures are drawn approximately half actual size. Broadly considered, the coaxial switch of our invention comprises a hollow metallic outer housing having integral main'and transverse portions adapted to connect with the outer conductor of standard coaxial transmission lines. Concentrically spaced within the outer housing and insulated therefrom is an inner conductor having main and transverse portions coaxial with corresponding portions of the outer housing.Y The transverse inner conductor serves as a radio frequency input lead integrally connected to the main portion of the inner conductor, which in turn is adapted to be selectively connected or disconnected to a standard coaxial transmission line. The inner conductor and outer housing are maintained in insulated coaxial relation by spaced dielectric walls interposed therebetween. Axially aligned fixed and movable conductive contact elementsare detachably mounted on the main portion of the. inner conductor and provide means, for '.'making and breaking a circuit through the switch. A vcuumized envelope, also detachably mounted on the inner conductor, encloses the fixed and movable 3 2,911,596 .Patented Dec. 15, 1959 contact elements, and pressure responsive means outside the envelope are provided to move the enclosed movable contact element to make or break a circuit through the switch.

In television and radio, there is a continuing need for coaxial switches capable of remote control, to effect fast shifting of circuits between various coaxial transmission lines. Thus, by the use of one of our coaxial switches, one or more transmitters may be routed to various antennas or dummy loads, at the discretion of the control engineer, or automatically as the result of a mechanical 'failure in the circuit. The switch is capable of handling many kilowatts on the television band or in lower frequencies, without causing. undue electrical disturbance in the transmission line due to its insertion.

In more specific terms, our,coaxial switch comprises a hollow copper outer housing corresponding to the outer conductor of a coaxial transmission line. The housing is T-shaped and split to provide two complementary parts 2 and 3, each part having integral main and transverse portions 4 and 6 respectively. The complementary parts are held together by releasable clamps 7, and in their assembled condition, shown in Fig. l,` the housing possesses a cylindrical cross-section. Each of the free ends of the T-shaped housing is provided with slots 8, definingA resilient free end portions 9, which cooperate with the clamps to connect the housing into a transmis-` sion line 1,0, shown in dash lines in Fig. 1. A snug slip t`between housing and transmissionline is insured' by providing a machined area 12 on the inner end surface of the housing. A shoulder 13 determines maximum interengagement of the housing with the associated transmission line.

Radio frequency energy is introduced into and distributed from the Yswitch by anyinner copper conductorl The input leadr16 of the inner conductorpis preferably cylindrical, and extends into the housing through the annulary dielectric wall 17 associated with the transverse portion of the housing.r At its inner end the input lead is integrally joined perpendicularly tothe main portionl 14 of the innerV conductor. The outer end of the input lead is adapted forconnection to aV source of radio frequency energy. The main portion of the innerconductor is preferably tubular and provided with internal threads 18 at each end. A transverse partition 19 within the tubular conductor, positioned midway between the ends thereof, divides the interior of the tubular inner conductor into two separate axially aligned and oppositely opening chambers 21 constituting piston cylinders. Each outer end of the tubular conductor is supported in coaxial relation to the-outer housing by a metallic annulus 22 which closely surroundsan end portion of the conductor. Bolts 23 demountably secure the annulus 22 to the inner side of the associated dielectric'wall 17, and also clamp' envelope 27, and at its vother end provided with a threaded cylindrical ange 28 adapted to engage the interior threads 18 in the open end of tube 14. The end cap structure ts snugly within the central aperture of the annular dielectric wall 17, which at once positions and secures the end cap structure against lateral displacement and vibration, and electrically insulates it from the outer housing.

Each end cap structure also provides a radially inwardly extending annular flange 29 adapted to slidably support a stem or piston rod 31, one end of which is integrally brazed to the closed inner end `32 of an expansible metallic bellows 33 extending into the glass envelope and having an open end 34 hermeticallybrazed to the end cap 25. The other end of piston rod 31 extends into the associated air cylinder 21, and is provided adjacent its end with a piston 36, reciprocable within the cylinder. Reciprocation of the piston effects inward and outward movement of the closed end 32 of bellows 33. A small diameter movable contact rod 37, preferably of tungsten, is integrally brazed on the bellows end 32, opposite to and axially aligned with the piston rod 3,1. The movable contact is selectively engaged and disengaged within the envelope 27 with a xed contact rod 38, also of small diameter tungsten rod and axially aligned with the movable Contact rod and hermetically sealed in the glass end wall 39 of envelope 27. Evacuation of the envelope is accomplished through tubulation 40. Outside the envelope, the fixed contact rod projects in a portion 41 adapted to be engaged by the inner conductor of a coaxial transmission line. The small diameter of opposed contact elements and their relatively wide 4spacing when open reduces to a negligible amount the open circuit capacitance between the contact elements. This is an important consideration as frequencies are increased because it tends to prevent undesirable transfer of energy to adjacent open circuits.

In order to reciprocate the piston 36, means are provided for admitting pressure air into the cylinders 21 on one side of the pistons. Fixed on the exterior of the outer housing by set screws 42, is a junction block 43, bored to provide air passages 44, each communicating at one end with an air line 46 connected to a source of air under pressure, and at the other end connecting with a passage 47 formed by glass tube 48 and port 49 opening into the conductor tube 14 behind the piston. As shown in Fig. v3, each glass tube is provided with a gasket 51 at each end to prevent leakage of air and also to form a resilient cushion for the glass. Vent hole 52 in each cylinder ahead of the piston communicates with the interior of the outer housing, which is at atmospheric pressure, and prevents the entrapment of air ahead of the piston. The use of compressed air to actuate the movable contact, and itsradmittance by means of a glass tube, insures a minimum disturbance inthe standing Wave ratio of the circuit, and also prevents formation of a conductive escape pathfor the considerable difference in potential between the inner conductor and the outer housing, which is at ground potential.

It will be apparent from Fig. 2 that envelope 27 With end cap 25 and movable and fixed contact rods may be detached as a unit from the inner conductor by releasing the flange 24 and disengaging ange 28 from threads 18. The impedance of the switch may then be increased or decreased by substitution of differently proportioned contact elements, designed to produce the desired impedance. For example, the switch illustrated is designed for a rated impedance of from 100 to 300 ohms, and operation at the lower frequencies. Efficient operation at higher frequencies may be achieved by substitution of contact elements having less impedance.

While the switch illustrated in Fig. 2 is of the normally closed type, it will of course be understood that the switch may be normally open or a combination of normally open-normally closed,vand still fall within the scope ofthe appended claims. Fig.Y 4 illustrates a combined normally opennormally closed switch, in which a coil compression spring 53, possessing suiicient resilience to overcome atmospheric pressure, 'is interposed between a 4 piston 36 and the associated end cap 25. The piston and vent hole 52 are relocated so that pressure air may be admitted into the chamber behind the piston to compress the spring and close the contacts, which are normally held open by expansion of the spring.

We claim:

1. A coaxial switch for coaxial transmission line circuits comprising a hollow metallic outer housing having integral main and transverse portions, an inner conductor having main and transverse portions coaxial with corresponding portions of the outer housing, a dielectric wall interposed between corresponding main and transverse portions of inner conductor and outer housing to retain them in insulated coaxial relation, axially aligned fixed and movable conductive contact elements detachably mounted on the main portion of the inner conductor, a vacuumized envelope detachably supported on the inner conductor and defining a vacuumized chamber about the contact elements, and pressure responsive means operatively connected to the movable contact element to selectively make or break a circuit through the main and transverse portions of the inner conductor.

2. The combination according to claim l, in which the hollow metallic outer housing comprises two separable complementary parts, and releasable clamp means are provided for normally retaining the parts in assembled relation.

3. The combination according to claim 1, in which said main portion of the inner conductor comprises a cylindrical tube transversely partitioned intermediate its ends to provide a pair of oppositely opening hollow chambers, and said fixed and movable conductive contact elements are detachably supported adjacent the open ends of the chambers and are responsive to pressure therein to make and break a circuit.

4. The combination according to claim 1, in which said fixed contact iselectrically insulated by a portion of the,

envelope from both the movable contact and the inner conductor in the open position of the contacts, and said movable contact is conductively related in all its positions with said inner conductor.

5. The combination according to claim 1, in which said vacuumized envelope includes a dielectric shell hermetically sealed at one end by a metallic end cap including an expansible metallic bellows, and the end cap and bellows are detachably mounted on the main portion ofthe inner conductor in conductive relation thereto.

6. The combination accordingto claim 3, in which dielectric tube means are provided interposed between the inner conductor and the outer housing tol communicate the interior of-each said hollow chamber with a source of air under pressure.

7. In a coaxial switch, a hollow metallic outer housingv having integral main and transverse portions, an inner conductor having main and transverse portions coaxial with corresponding portions of the outer housing, said main portion of the inner conductor comprising a cylindrical tube transversely partitioned intermediate its ends to provide a pair of oppositely opening hollow chambers constituting piston cylinders, and a vacuumized envelope comprising a dielectric shell hermetically sealed at one end by a metallic end cap including a mechanically ex`- pansible metallic bellows.

8. The combination according to claim 7, in which annular dielectric wallmeans are provided interposed be tween the inner conductor and outer housing to retain the inner conductor in spaced concentric relation Within the outer housing.

9. The combination according to claim 7, in which a pressure responsive piston and stem are operatively interposed between said bellows and said piston cylinders to effect selective expansion and contraction of the bel# lows.

10. The combination according to claim 7, in which a 5 6 Contact element is integrally brazed on one end of the 2,642,495 Haulrnan et al June 16, 1953 bellows within the envelope and is movable therewith. 2,690,540 Boothby Sept. 28, 1954 2,740,868 Jennings Apr. 3, 1956 References Cited 1n the file of thxs patent 2,740,869 Jennings Apr. 3, 1956 UNITED STATES PATENTS a 2,762,881 Brockweu et a1 sept. 11, 1956 1,892,538 Prince Dec. 27, 1932 y2,794,087 Jennings et al May 28, 1957 

